Hi TMCD,
I would add one additional requirement to Dan’s excellent list, and that is Security which should not be confused with ‘Tightness’.
In the slipstream atop a vehicle travelling at highway speeds, wind force even on an open structure like a ladder is substantial. Add to this massive turbulence, and you have a recipe for the creation of really serious ‘flogging’ which can be the downfall of even the tightest of knots. So you are also going to have to give a moments thought to making this binding SECURE.
First up - Cordage. For this job you need tightness, and although using very strong bungee cord it might seem that you have your ladders tight, think about when a gust of wind from a truck coming the other way hits your load. The elasticity in the bungee will allow your ladders to lift and in doing so will be subject to an even greater lifting force which can have the potential of ripping the bungee right off the roof rack. My advice would be to go and purchase a length of good quality 8mm braid. It will be way stronger than you need, flexible even in the cold, have good abrasion resistance and be very easy to tie knots in and ‘pull through’. Also, if you are doing this regularly, I would consider fixing a thick rubber pad on the vertical upright bar of your roof rack to give a bit of padding for your ladder against the metal of the rack.
Next, think about the forces that are going to be put on the ladder. As you start or stop, the ladder is going to want to slide backwards or forwards. As you corner it is going to want to slide from one side to the other and it may also want to slide crosswise i.e. front sticking out one side and the back sticking out the other side - a bit like a jousting lance. Then finally, the wind hitting the front of the vehicle is rushing upwards and trying to lift the front of the ladder up and into the sky. This last force can be substantial, so don’t block the flow of air through the rungs by putting planks onto the rungs forward of the screen - it might only be a small ‘sail’ but with wind speeds capable of exceeding 100mph the force that small sail can generate is massive.
With all this in mind, you can tie down your ladder securely and quickly with just three binding points, while ticking all the required boxes.
Start off by making a loop knot around the front upright plate (under the bar). I used to use an Eskimo bowline because it was so easy to make from a slipped overhand knot, but I now use a Carrick loop since I discovered the Chinese Button knot method of tying it (that’s another post). Make the loop small with about 2ft to 3ft of spare ‘end’.
Lay the ladder on the rack snug up against the side plate and take a bight of rope down between the rungs, forward under the rack cross bar, up between the rungs and pull the bight over the side plate. Pass the end up through this bight loop and half hitch the end back to itself to hold the bight loop in place.
Make a second bight loop in the SP and pass it over the other leg of the ladder, down and around the rack cross bar and back up across the ladder leg towards the side plate. Use the end again, to pass it through the bight loop and half hitch it to itself. Haul the bight tight by pulling on the SP.
Make a slipped OH loop half way between the front and back cross bars as the start of a tensioning hitch.
At the back cross bar, make a long bight, pass it down under the rung near the back cross bar, under the cross bar, out the side and around the side plate, under the ladder and back up the hole it just went down. Pull the bight right up to the slipped OH, pass it through the slipped loop and fasten it to self with two half hitches, having first hauled tight to tension the whole affair.
The only job left to do is to tidy up any remaining rope to make sure it does not drag on the road or get flogged by the wind. Either bag the xs rope and fix the bag to the ladder with a bungee, or coil the xs and half hitch it to the ladder.
Derek
